Using holograms to provide some level of document security is well known. For example, many bankcards carry a holographic image of the authentic card user, so that the identity of that user can be verified. In other cases, holograms are embedded within security documents, so that they are invisible to the unaided eye. To verify or authenticate such documents, the hologram has to be irradiated with light of a suitable wavelength. Depending on the wavelength used, the holographic image can either be viewed directly or it can be sensed and imaged using suitable imaging techniques.
In the drive towards increased security, many hologram based validation or authentication techniques are becoming more complex. However, a problem with increasing the complexity of security is that it almost invariably increases the complexity of the procedures required to manufacture the security device and/or the hologram itself. This limits the use of such systems, particularly for applications where mass manufacture techniques are needed in order to make the devices commercially viable.